Cylindrical audio plugs and corresponding jacks have been used for many decades to establish connections for electrical signals bearing audio information. Typically the equipment that either produces or records the signal would include a jack, and the peripheral equipment such as headphones or microphones would include the plug. Whereas the older audio plugs were one-quarter inch (6.35 mm) diameter, newer and smaller equipment such as Compact Disk (CD) players, MP3 players, and mobile telephone handsets use the nominally 3.5 mm (nominally ⅛″) plugs and jacks.
In the past few years smartphone-type mobile telephone handsets, which have greatly increased capability in so far as video and audio processing power have proliferated in many markets including the U.S. Smartphones have very streamlined external designs typically including, for example, no more than two physical buttons, e.g., a power button and a volume rocker switch, and typically include no more than two external connectors including a combined data transfer and charging connection (e.g., Universal Serial Bus (USB) jack) and an audio jack. The streamlined, limited external design complexity of smartphones including the limited number of buttons and connectors is part of the current design paradigm which is compensated by the highly versatile user controls that can be achieved through non-physical touch screen GUI control elements.
However, the availability of only a small number of connectors on a smartphone while simplifying the user experience can be quite limiting. For example, there is a sophisticated type of audio known as binaural audio. Recording binaural audio requires two separate microphones. The two microphones can be located on a model head which is intended to reproduce the acoustics of a person's head. The two microphones can also be incorporated into earphones. The intent is two capture differences in time of arrival, and volume of sounds reaching a person's two ears so as to capture the sensation of direction of emanation of a sound. In other words to create a three dimensional (3-D) sound effect.
Another audio technology that utilizes two microphones is a certain class of noise cancellation systems. In such systems one microphone is located close to a speaker's mouth and a second microphone is located further away. Both microphones will pick up ambient noise, but the microphone closer to the person's mouth will have a stronger component of the speaker's voice. The signal obtained from the further microphone can be subtracted from that received from the closer microphone in order to reduce the noise component. The noise cancellation systems and the binaural systems can be built into a set of headphones or earphones that include two (stereo) speakers, i.e., one for each ear. In such cases two speaker channels, plus two microphone channels plus a ground connection will be required. Unfortunately, most commonly available audio plugs and jacks have four or less contacts.
Additional contacts could also be used to implement differential signaling from a microphone (as opposed to using a single wire referenced to ground). Differential signal reduces noise pickup in long leads. Yet another use of an additional contact would be to supply power to the device that includes the jack, e.g., for charging or to supply power to the audio accessory that includes the plug, e.g., for powering electrical circuits therein.
While there have been prior attempts to add a fifth contact to a plug without increasing the standard length of 3.5 mm plugs, the problem is that such plugs and the jacks made to work with them are not fully backward compatible with preexisting three-contact and four-contact plugs and jacks. This is an issue because devices that include jacks such as smartphones and devices that include plugs such as high end headphones are not necessarily sold together. A purchaser of a smartphone with a five-contact jack may own one or more sets of expensive headphones including separate ones designed for web chats and separate ones designed for listening to music that are equipped with three-contact or four-contact plugs. Similarly a person owning an expensive headset equipped with binaural microphones or noise cancellation and a five pole plug may want to use that with multiple devices that have jacks with four or less poles.
FIG. 22 is a cross sectional view of prior art plug disclosed in PCT patent publication WO2010021072 A1, published Feb. 25, 2010. The disclosed plug 10 appears to be equivalent to what has been implemented in the Sony® Xperia 2 and 3 smartphones. The approach used in this prior art design is to squeeze four contacts 12, 13, 14, 15 separated by insulating portions 22, 23, 24 into the space that would normally include only three contacts in a normal four-contract audio plug. This reduces the margin for error, and, due to real world manufacturing tolerances and design variations, a four-contact plug inserted into a jack designed for this five-contact plug may not function due to a contact of the jack touching two of the contacts of the four contact plug or resting on an insulating region between the contacts. Due to all of these issues it becomes very difficult or impossible for detection circuits that are currently used in smartphones to correctly detect such a plug.
What is needed is a five-contact audio plug that works with a five-contact audio jack that is backward compatible with three-contact and four-contact audio plugs. It would also be desirable that the five-contact audio plug be backward compatible with three-contact and four contract audio jacks.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.